DISTRIBUTION AND HAZARD ASSESSMENT OF COLLAPSES AND LANDSLIDES IN SICHUAN-TIBET TRAFFIC CORRIDOR

The Ya'an to Nyingchi section of the Sichuan-Tibet traffic corridor is located in the southeast of the Qinghai-Tibet Plateau. The project region is characterized by complex geological conditions,strong river cutting,fragile geological environment,active neotectonic movement,high mountains,deep valleys and poor slope stability. It is one of the areas with the most developed and serious hazards of collapses and landslides in China. In order to guarantee the smooth construction and safe operation of the related project in the corridor,this study takes the first order watershed on both sides of the line as the boundary,and obtains a total of 4509 collapses and landslides in the Ya'an-Nyingchi section of the Sichuan-Tibet traffic corridor through remote sensing interpretation and field investigation. On this basis,a total of nine factors,including elevation,slope,aspect,engineering geological strata,fault,river,road,peak ground acceleration and rainfall are selected to analyze the spatial distribution law and development characteristics of disasters. Then it establishes a coupling model of frequency ratio method and logistic regression method to evaluate the hazard of collapses and landslides for the major traffic corridor project in plateau mountainous area. The study results show that: (1)The areal density of collapses and landslides in various counties along the corridor shows a spatial decreasing trend from west to east. (2)The conditions conducive to disasters occurrence include elevation of 1~4 km,slope gradient steeper than 20°,aspects of S,SW and W,rock groups of soft,hard and very hard,within 6.4 km of fault,within 3.2 km of river,within 800 m of road,peak ground acceleration of 0.20g and average annual rainfall more than 1100 mm. (3)The hazard of study area is divided into five grades: very low hazard(18.64%),low hazard(26.18%),medium hazard(24.75%),high hazard(19.82%),and very high hazard(10.61%),where the very high hazard and high hazard areas are mainly distributed near the faults and in the areas with steep slopes. (4)The AUC value of the coupling model reaches 0.737,which is better than that of the single frequency ratio model 0.712,indicating that the evaluation result of the coupling model has higher accuracy. This study can provide an important reference for disaster prevention and mitigation in the planning,construction and future operation of the related project in Sichuan-Tibet traffic corridor.